1. Field of the Disclosure
This specification relates to an earth leakage circuit breaker, and more particularly, to an earth leakage circuit breaker which can be operated by determining whether harmonic waves (harmonics) have been included in an earth leakage signal or not, based on a determination signal generated by tracking the earth leakage signal applied thereto.
2. Background of the Disclosure
FIG. 1 is a block diagram illustrating a circuit configuration for a trip operation of an earth leakage circuit breaker in accordance with the conventional art.
As shown in FIG. 1, in the conventional earth leakage circuit breaker, once an earth leakage signal is sensed by a zero-phase current transformer (abbreviated as ZCT hereinafter), the earth leakage signal is amplified by an amplifier. The amplified earth leakage signal is compared with a reference voltage set by a level discriminator. If the amplified earth leakage signal is greater than the reference voltage, a trip signal generator transmits a trip control signal to a trip mechanism. The trip mechanism triggers a switching mechanism to a trip position (i.e., an automatic circuit breaking position), and the switching mechanism breaks (disconnects) an electric circuit. Under such configuration, an electric load and a human body can be protected when current leakage occurs.
In the conventional earth leakage circuit breaker, a malfunction does not occur on a circuit to which a linear load not having noise or distortion is connected. However, most of electronic and electric devices adopting alternating current (abbreviated as AC hereinafter) electric power do not directly use AC, but convert the AC into a direct current (abbreviated as DC hereinafter). During such conversion, a switching device is used to enhance efficiency. Due to such switching operation, a pure AC signal has noise, and the AC signal is distorted. That is, even if an earth leakage signal does not occur, harmonics due to switching noise and signal distortion are detected by a ZCT, in a similar manner to the earth leakage signal, because unbalancing among phases occurs on the AC signal. In the conventional art where only levels of signals are compared with each other, a trip operation may be erroneously performed due to noise or harmonics greater than a reference voltage.